Many negative pressure storage or process tanks and, in particular, older tanks, are equipped with manholes that include covers that open outwardly with regard to the tank. Typically, the cover is bolted to a flange that encircles the outside of a cylindrical manway. The term manway, as herein used, refers to a tubular member that is welded or otherwise joined to the tank to provide access into the tank.
Replacing a manhole with a bolted-on blind flange within a negative pressure storage tank with a more preferred hinged door assembly has heretofore presented certain structural difficulties where the existing manway is removed from the tank and replaced with an entirely new manhole unit.
Complete removal of the existing manhole can produce structural damage to the tank shell in and about the manway opening that oftentimes requires extensive repair to the tank. Furthermore, retrofitting a new manway to the repaired opening is sometimes difficult and can result in damage to existing tank coatings, linings or insulation.